Incidentally I spend far too much time playing computer games and yet I only just learnt what S meant by playing Bloodborne. And only then by looking it up online. That was in relationship to weapon scaling by stats and you had to search for it. 35 years of computer gaming. Never heard of S before.
What the heck games were you playing for 35 years that you never came across this? Like, seriously. I was familiar with it by, what, 1992? 1994? Something like that.
Did you just never play console games or something? Or never play Japanese games?
Basically almost any Japanese console game that gave any kind of letter ranking, from like, the late 1980s onwards (so yeah, about 35 years) has had S as the top ranking. That particularly includes racing games and fighting games, but also includes a ton of other stuff.
And on top of that, for fifteen plus years, gamers have discussed things as being in "tiers", and for most of that time, those tiers have typically been either numerical, or letters, and if letters, with S at the top. This isn't a new thing. If you've played any kind of competitive game with multiple characters to choose from, there will have been discussion of tiers - and very often that discussion involves the term S-tier. Sometimes it's substituted with "God tier".
It's certainly ubiquitous within certain genres of video games, so it is very surprising that you've missed it for so long. Even not playing those genres it would be surprising that you didn't see some attempted list involving it.
For an amusing take on this kind of Tier list, see TierZoo, where the channel rates animals in very much the same manner: